The present invention relates to a contour emphasizing circuit, wherein a digital contour-emphasized video signal, on the basis of the input of an analog signal, is output, and is employed to produce contour-emphasized color video signals by a display device (for example, matrix type display device) which is digitally driven, such as a plasma display (referred only to as PDP) and liquid crystal display (referred only to as LCD).
In conventional CRT (Cathode Ray Tube) display device, contour emphasizing processing is carried out to achieve high picture quality implementation and high-pass characteristic compensation. The contour emphasizing circuit for carrying out this contour emphasizing processing is, as shown in FIG. 1, composed of a Y/C separation circuit 10, a color demodulation circuit 12, a contour extracting circuit, phase adjustment circuits 16, 18 and 20, an adder 22 and a matrix circuit 24.
The Y/C separation circuit 10 separates a Y (luminance) signal and a C (color) signal from the composite video signal (for example, compound color television signal) input to an input terminal 26, and the color modulation circuit 12 separates a Y signal, an Rxe2x88x92Y (color difference) signal and a Bxe2x88x92Y (color difference) signal on the basis of a Y signal and a C signal.
The contour extracting circuit 14 extracts the contour component Ye which is a high-pass component of a video signal on the basis of an adder 22.
The matrix circuit 24 prepares a signal adding the contour component Ye to the R (red), G (green) and B (blue) signals, respectively, on the basis of (Y+Ye) signals added by the adder 22, an (Rxe2x88x92Y) and a (Bxe2x88x92Y) signal phase-adjusted by phase adjustment circuits 18 and 20. That is to say, the matrix circuit 24 prepares R+Ye, G+Ye and B+Ye on the basis of the operations in following equations (1), (2) and (3). By outputting these R+Ye, G+Ye and B+Ye to the CRT-display device by means of output terminals 28r, 28g and 28b, videos contour-emphasized by this CRT display device are displayed.
(Rxe2x88x92Y)+(Y+Ye)=R+Yexe2x80x83xe2x80x83(1)
(Gxe2x88x92Y)+(Y+Ye)=G+Yexe2x80x83xe2x80x83(2)
(Bxe2x88x92Y)+(Y+Ye)=B+Yexe2x80x83xe2x80x83(3)
(Gxe2x88x92Y) in the above equation (2) is generated by the following equation (4).
When a video contour-emphasized by the matrix type display device driven by digital video signals (for example, R, G and B signals) like PDP and LCD is displayed, each signal of (R+Ye), (G+Ye) and (B+Ye) obtained in output terminals 28r, 28g and 28b in FIG. 1 is output to the display device after being digitized by the A/D (analog/digital) conversion circuit. However, in such a prior example, when a large amplitude signal is input to an input terminal 26, or when the contour emphasizing quantity (or contour emphasizing coefficient, the description is omitted, as it is similar afterwards) is xe2x80x9clargexe2x80x9d, there is a problem that the correct operation cannot be obtained over the dynamic range of the A/D conversion circuit.
For example, when a large amplitude signal is input to the input terminal 26, by outputting a signal over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG. 2(a) from output terminals 28r, 28g and 28b, there are problems that signals exceeding an upper conversion reference voltage value VRT (for example, 5 volts) in the dynamic range, as shown at the right-hand in said FIG. (a), are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRT (for example, 3 volts) in the dynamic range are cut, resulting in producing black crushing.
Further, when the contour emphasizing quantity of the contour extracting circuit 14 is xe2x80x9clargexe2x80x9d, there are problems that signals over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG. 2(b) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRB are cut, resulting in producing black crushing.
The present applicant simultaneously proposes a contour emphasizing circuit as shown in FIG. 3 as a separate application to solve the above mentioned problems. That is to say, by generating a Y signal after converting analog color video signals to digital signals by the A/D conversion circuit and by constituting so that digital video signals which are contour-emphasized will be obtained from adding the contour component extracted from this Y signal to digital color video signals from the A/D conversion circuit, it has been designed so that the contour emphasizing component, unlike the conventional example, will not surpass the dynamic range of the A/D conversion circuit.
However, when a signal processing circuit is added to carry out the signal processing like picture element number, gamma correction, etc. to this proposed contour emphasizing circuit, there is a problem that the contour emphasizing effect is reduced by half according to the position for adding this signal processing circuit.
For example, as shown in FIG. 3, when the signal processing circuit 35 for carrying out the picture element number conversion and gamma correction is added to the back stage of contour adders 34r, 34g and 34b, there is a problem.
The circuit shown in FIG. 3 is constituted by A/D conversion circuits 30r, 30g and 30b, a first phase adjustment circuit 31 composed of line memories 31r, 31g and 31b, a second phase adjustment circuit 33, contour adders 34r, 34g and 34b, a signal processing circuit 35, a Y signal generation circuit 36, a contour extracting circuit 38, a gain controller 40 for the contour components, and a coefficient multiplication circuit 42.
Hence, analog R, G and B signals input to input terminals 44r, 44g and 44b are converted to digital signals by A/D conversion circuits 30r, 30g and 30B, phase-adjusted by first and second phase adjustment circuits 31 and 33, and input to contour adders 34r, 34g and 34b. The Y signal generation circuit generates Y signals from digital R, G and B signals, the contour extracting circuit 38 extracts a contour component from a Y signal, this extracted contour component enters in contour adders 34r, 34g and 34b through the gain controller 40 and the coefficient multiplication circuit 42, and are added to the original digital R, G and B signals. For digital R, G and B signals contour-emphasized by those contour adders 34r, 34g and 34b, the signal processing like picture element number conversion, gamma correction, etc. is carried out by the signal processing circuit 35 and supplied to the display device through output terminals 86r, 86g and 86b, and contour-emphasized videos are displayed.
At this time, contour adders 34r, 34g and 34b add contour components as shown in the same figure (b) output from multipliers 86r, 86g and 86b of the coefficient multiplication circuit 42 to input signals R, G and B as shown in FIG. 4(a) from the second phase adjustment circuit 33, and output R, G and B signals contour-emphasized as shown in the same figure (c). However, there is a problem that the contour emphasizing effect comes to be reduced by half by the signal processing circuit 35 at the later stage.
Next, functions that the contour emphasizing effect as described above is reduced by half will be explained employing FIGS. 5 and 6. FIG. 5 shows a case that the picture element number conversion is carried out to adjust the sampling picture element number to the display picture element number of the display device, and if the rate conversion is carried out making the sampling picture element number to xc2xd, as shown in the same figure (b), against the original signal shown in the same figure (a), signals output from output terminals 86r, 86g and 86b become as shown in the same figure (c). Since this output signal causes, as shown in FIG. 5(c), a difference in step, resulting in a deviating linearity, as well as becoming a different signal from the original signal in terms of balance of undershoot and overshoot, and when a video is displayed by supplying it to the display device, there is a problem that even though contour emphasis is carried out, the contour emphasizing effect comes to be reduced by half giving an unnatural property to the videos. In FIG. 5(b) and (c), S1 through S4 express sampling points, U1 expresses the size of the undershoot, and O1 expresses the size of the overshoot.
FIG. 6 shows a case where gamma correction is carried out to correct the display characteristic of the display device, and if gamma correction employing the input-output signals shown in the same figure (b) against the original signal shown in the same figure (a) is carried out, signals outputted from output terminals 86r, 86g and 86b become as shown in the same figure (c). As shown in FIG. 6(c), since the undershoot and overshoot become completely different values from the proper reasonable value that the undershoot and overshoot show in the same figure (a), there is a problem that dislocation is produced in the contour emphasizing component and the contour emphasizing effect comes to be reduced by half. In FIG. 6(c), U2 expresses the size of undershoot, and 02 expresses the size of overshoot.
The present invention has been carried out taking into account problems as described above, aims at providing a contour emphasizing circuit that can prevent the contour emphasizing effect from being reducing by half by the added signal processing circuit, as well as contour emphasized videos without white crushing or black crushing can be displayed by a display device driven by digital video signals, when a large amplitude signal capable of producing white crushing or black crushing by the contour emphasizing circuit in FIG. 1 is input and also when the contour emphasizing quantity is enlarged.
The contour emphasizing circuit according to the present invention is characterized by being provided with an A/D conversion circuit for converting analog color video signals (for example, R, G and B signals) to digital color video signals, a signal processing circuit for carrying out signal processing like picture element number conversion, gamma correction, etc. to an output signal of this A/D conversion circuit, a Y signal generation circuit for generating a Y signal from an output signal of this signal processing circuit, a contour extracting circuit for extracting a contour component from the generated Y signal, and a contour adder for outputting a contour-emphasized signal from adding this extracted contour component to an output signal of said signal processing circuit.
Since a Y signal is obtained after converting analog color video signals to digital signals by the A/D conversion circuit and a contour component extracted from this Y signal is added to digital color video signals output from the signal processing circuit, the contour emphasizing component, unlike the conventional example, does not surpass the dynamic range of the A/D conversion circuit. For this reason, when analog color video signals input to the contour emphasizing circuit of the present invention are large amplitude signals, or even when the contour emphasizing quantity is enlarged, neither white crushing nor black crushing is produced when the contour emphasizing video outputting a signal from the contour emphasizing circuit of the present invention to the display device driven by digital video signals is displayed. Further, the contour adder is placed behind the signal processing circuit and it has been designed to add a contour component to digital video signals after carrying out the signal processing like picture element number conversion, gamma correction, etc., influences to a contour component by the signal processing like picture element conversion, gamma correction, etc. can be carried out, preventing the contour emphasizing effect from being reduced by half.
Hence, said Y signal generation circuit is not limited to generating a Y signal from an output signal of the signal processing circuit, but may also generate a Y signal from an output signal of the A/D conversion circuit.
Further, said signal processing circuit may be constituted by two signal processing circuits of a picture element number conversion circuit for carrying out the picture element number conversion and a gamma correction circuit for carrying out the gamma-correction circuit, and it may be constituted by a signal processing circuit of one side of a picture element number conversion circuit and a gamma-correction circuit.
Further, to be able to display videos having emphasized contours in the vertical direction and horizontal direction from video signals having an added vertical contour component and horizontal contour component, the contour extracting circuit is constituted by first and second line memories, a vertical contour extracting circuit, a contour emphasizing frequency setting circuit, a horizontal contour extracting circuit and a contour synthesis circuit.
Further, to simplify the circuit configuration of the contour emphasizing frequency setting circuit, the contour emphasizing frequency setting circuit is constituted by four 1-dot delay elements connected in series. A Y signal of 2-dot delay is output from the second 1-dot delay element, and a Y signal of 4-dot delay is output from the fourth 1-dot delay element.
Further, to eliminate noise, in the contour extracting circuit, a core ring circuit for suppressing a contour component of less than a certain level is installed.
Further, to be capable of enlarging the contour emphasizing quantity, a gain controller for adjusting for output the size of the contour component extracted by the contour extracting circuit and a coefficient multiplication circuit outputs to the contour adder, multiplying coefficients Kr, Kg and Kb of less than 1 to its output signal.